MONFRINO, Giovanni (Corso Giovanni Agnelli 200, Torino, I-10135, IT)
PALAZZETTI, Mario (Corso Giovanni Agnelli 200, Torino, I-10135, IT)
RE FIORENTIN, Stefano (Corso Giovanni Agnelli 200, Torino, I-10135, IT)
MONFRINO, Giovanni (Corso Giovanni Agnelli 200, Torino, I-10135, IT)
PALAZZETTI, Mario (Corso Giovanni Agnelli 200, Torino, I-10135, IT)
| CLAIMS 1. A wheel assembly for vehicles comprising a wheel rim having a" symmetry axis and two reciprocally and axially spaced peripheral annular portions, an annular body comprising a tread adapted to roll in contact with a road surface and a reinforcing band of said tread made of elastomeric material, and structural connecting means connecting said wheel rim to said annular body, characterized in that said structural connecting means comprise at least first and at least second tie-rod means extending from said peripheral portions of said wheel rim and converging towards an intermediate annular band of said annular body spaced from both axial end edges of said annular body. 2. An assembly according to claim 1, characterized in that said first and second tie-rod means are firmly connected to said intermediate band of said annular body. 3. An assembly according to claim 1 or 2, characterized in that said intermediate band is a middle band of said annular body. 4. An assembly according to any one of the proceeding claims, characterized in that said intermediate band is delimited by two intermediate planes orthogonal to said axis and each arranged at a given distance from said one corresponding peripheral axial end edge. 5. An assembly according to claim 4, characterized in that the annular body comprises two side portions opposite to the axial ends, each of which is delimited by said one corresponding edge and overhangingly protrudes from at least said one corresponding intermediate plane orthogonal to said axis. 6. An assembly according to any one of the preceding claims, characterized in that said first and second tie-rod means transmit actions in directions forming a varying angle from five to eighty- five degrees with said axis. 7. An assembly according to any one of the claims from 1 to 6, characterized in that said first tie-rod means intersect said second tie-rod means on said annular body. 8. An assembly according to any one of the proceeding claims, characterized in that said first and second tie-rod means reciprocally intersect on a middle plane of said annular body orthogonal to said axis and arranged at the same distance from said axial end edges . 9. An assembly according to any one of the preceding claims from 1 to 6, characterized in that said first and second tie-rod means are each coupled to said annular body at a corresponding axial boundary of said intermediate zone . 10. An assembly according to any one of the preceding claims, characterized in that it further comprises third tie-rod means extending between said annular body and said wheel rim and between said first and second tie-rod means. 11. An assembly according to any one of the preceding claims, characterized in that said tie-rod means comprise elongated wire or cable means. 12. An assembly according to any one of the preceding claims, characterized in that said tie-rod means comprise membrane or link means . 13. An assembly according to claim 9, characterized in that said cable means comprise for each of said peripheral portions at least one corresponding continuous cable wound on first attachment elements carried by said wheel rim and on second attachment elements carried by said tread. 14. An assembly according to any one of the preceding claims, characterized in that it comprises for each of said peripheral portions a corresponding membrane body for closing the space between the corresponding peripheral portion and said one corresponding annular end edge of said tread. |
TECHNICAL FIELD The present invention relates to a wheel assembly for vehicles, specifically for motor vehicles. BACKGROUND ART
In the field of tyres for vehicles it is known from patent application WO 2005/082643 Al, filed by the same applicant, to make an airless tyre of the type comprising a tread; two beads made of elastomeric material for attachment to a wheel rim; and two sidewalls, each of which comprises a corresponding structural annular membrane tensioned between the corresponding sidewall of the tread and the corresponding bead, so as to be pre-tensioned in the absence of loads on the tyre. The generatrixes of the membranes reciprocally converge and meet in an external point far from the tread. The known tyres of the above-described type further comprise at least one tubular reinforcing body coupled to the tread and made of material other than the elastomeric material, normally harmonic steel or fiber- reinforced plastic material, which is of the either corrugated or ribbed type and has a length essentially equal to that of the tread so as to extend between one sidewall and the other of the tyre.
The known tyres of the above-described type, although applied, are not fully satisfactory for the following reasons. Firstly, the specific arrangement and the manufacturing method of the side annular membranes limit the increase of tyre strength to side stresses, i.e. to stresses parallelly directed to the axis of the tyre itself. This is the direct consequence of the fact that the membranes have generatrixes which reciprocally converge and which intersect in points which are, in some cases, external to the tread and which are, in other cases, internal to the tyre, but are always, in all cases, radially very far from the tread itself. As a consequence, when the tyre is stressed by side components or loads directed parallelly to the rotation axis of the tyre itself, the portion of the tread arranged in contact with the road surface acts as an oscillating body about a fulcrum or hinge instantaneously defined by the mentioned different intersection points. By increasing the components parallelly directed to the axis, i.e. the side load, the tyre - responds by deforming but, above all, by moving sideways and partially lifting from the ground in an unpredictable manner, compromising at a certain point the vehicle stability.
Furthermore, again in the known solutions, the tubular reinforcing body associated to the tread is difficult to be dimensioned because, on one hand, it must have high stiffness to support the radially directed load without exceeding predetermined deformation limits but, on the other hand, it must be as flexible as possible to allow to easily overcome any obstacle in the absence of load peaks. As a consequence, the result of the dimensioning always arises from accommodations or choices with the consequence that the tread is not often able to adapt and behave in a different manner according to the type of obstacle and/or curvature of the line travelled by the tyre.
For the aforesaid reasons, the pressure distribution on the ground is all but homogenous, as desirable for an optimal grip, and however has a relatively high average value .
Finally, the tubular body increases the weight of the tyre and as it is normally complex from a constructive point of view and made of specific materials, it considerably contributes to raise the final cost of the tyre.
DISCLOSURE OF INVENTION
It is the object of the present invention to provide a wheel assembly for vehicles, which features allow to simply and cost-effectively solve the problems mentioned above.
According to the present invention, a wheel assembly for vehicles is made, comprising a wheel rim having a symmetry axis and two reciprocally and axially spaced peripheral annular portions, an annular body comprising a tread adapted to roll in contact with a road surface and a reinforcing band of said tread and made of elastomeric material, and structural connecting means connecting said wheel rim to said annular body, characterized" in that said structural connecting means comprise at least first and second tie-rod means extending from said peripheral portions of said wheel rim and converging towards an annular intermediate band of said annular body spaced from both axial end edges of said annular body.
Preferably, in the above-described wheel assembly, said first and second tie-rod means are firmly connected to said intermediate band of said annular body and conveniently to a middle band of said annular body. BRIEF DESCRIPTION OF THE DRAWINGS "
The invention will now be described with reference to the accompanying drawings, which show a - non- limitative embodiment thereof, in which:
- figure 1 is a perspective view of a preferred embodiment of a wheel assembly according to the present invention mounted on a vehicle; - figure 2 is a diagrammatic perspective view, with parts removed for clarity, of the wheel assembly in figure 1; figure 3 diagrammatically shows the tyre in figure 1 partially in section,- - figures 4 and 5 are figures similar to figure 3 and show two different variants of a detail in figure 3 ; figure 6 shows a chart comparing the force pattern exchanged between a hub and a tread in the presence of an obstacle defined in the case of the wheel assembly in figure 1 and in the case of a traditional wheel assembly; and figure 7 shows a chart comparing the side displacement pattern of the tread according to the side load transmitted to the tread itself in the case of the wheel assembly in figure 1 and in the case of a traditional wheel assembly.
BEST MODE FOR CARRYING OUT THE INVENTION In figure 1, numeral 1 indicates as a whole a wheel assembly for a vehicle 2, specifically a motor vehicle. The wheel assembly 1, which is able to support the vehicle 2 without needing to be pressurized with air or other pressurized fluids, has a rotation axis 3 and comprises a wheel rim 4 (figures 1 and 2) coaxial to the axis 3 and, in turn, comprises a central attachment portion to a hub of the vehicle 2 and two annular radial flanges 6 with axial ends (only one of which is shown in figure 19) protruding from the portion 5. The whole assembly 1 further comprises an annular body 7 made of elastomeric material, which in the absence of stress extends coaxially to the axis 3 in a position radially spaced from the wheel rim 4 and comprises a tread 8 externally delimited by a rolling surface 9 in contact with the road surface, and a tubular reinforcing portion 10 (figure 2) , per se known and described in detail in patent application WO 2005/082643 Al, which is therein integrally quoted for completeness of description for the necessary parts. Specifically, the tubular reinforcing portion 10 is arranged within the tread 8 and has a dimension parallelly measured to the axis 3 essentially equal to that of the tread 8 measured in the same direction, and a differentiated, predetermined stress strength, i.e. depending on the stress to which it is subjected. Conveniently, the tubular reinforcing portion 10 comprises (figure 2) a continuous, external annular belt 12 integrally connected to. the internal surface of the tread 8, in a manner known per se, and provided with a plurality of threads or fibers, either weaved or not, embedded in the elastomeric material to support the circumferential tensioning actions. The tubular reinforcing portion 10 further comprises a plurality of plugs 13 (figure 2) , which are carried by the belt 12 and which protrude towards the wheel rim 4 to exert a resisting action with respect to the circumferential compression actions when the tread 8 is rolling. Again with reference to figure 1 and to figure 3, the annular body 7 is directly connected to the wheel hub 4 by means of a structural tie-rod assembly 15. In the specific example described, the structural assembly 15 is of the type with wires or cables, either pre- tensioned or not, and comprises, for each radial flange 6, a corresponding crown 16 of fastening portions 18, conveniently eyelet-shaped, coupled to an external peripheral edge of the corresponding flange 6 in reciprocally and equally spaced positions. The structural assembly 15 also comprises a further crown 19 of attachment elements 20, which are anchored to the annular body 7, extend towards the wheel rim 4 from an internal surface of the tubular body 7 and lay on a common radial middle plane M orthogonal to the axis 3 and arranged at the same distance from the opposite axial edges 7a of the external annular body 7. The fastening portions 18 of the same flange 6 are connected to the attachment elements 20 by means of a single continuous wire element 21, conveniently either a plied steel wire or other equivalent elongated element, which has an end firmly connected to the wheel rim 4 and, for the whole circumference of the corresponding flange 6, in sequence, passes through a first fastening portion 18, extends towards the mentioned middle plane M, is either coupled or firmly connected to a corresponding first attachment element 20, and returns towards the corresponding flange 6 to cross a second fastening portion 18 of the corresponding crown 16 which is consecutive to the first fastening portion 18, and to advance, as previously shown, towards a second attachment element 20 adjacent to the first attachment element 20 to form a corresponding continuous seam 22 to be then blocked on the wheel rim 4. In this manner, the two continuous wire elements form corresponding series 23 of inclined spokes 24 each forming a varying angle A between 5 and 85 degrees with a plane parallel to the middle plane M according to the variation of the distance between the wheel rim and the tread. As shown in figure 1, and specifically in figure 3, each spoke 24 of one of said series 23 of spokes converges towards a point thereof, indicated by numeral 25 in figure 3, where it intersects a corresponding spoke 24 of the other series of spokes 23. Specifically, in the example described, the points 25 " are part of a crown 19 of points which all lay on the middle plane M and on the annular body 7 (figure 3) .
In this manner, the side loads acting on the annular body 7 are transmitted to the wheel plate 4 only by the inclined spokes 24 and, thus, only along the predetermined, inclined directions of the angle A. Again with reference to figure 1, the wheel assembly 1 finally comprises two non-structural membranes 27 each arranged between a corresponding radial flange 6 and a corresponding edge 7a of the annular body 7 only to isolate the seams and the space defined therebetween from the outside.
In the variant shown in figure 4, two crowns 19 of attachment elements 20 are provided, which are spaced from the middle plane M and lay on corresponding intermediate planes Pl and P2 always orthogonal to the axis 3 and parallel to the middle plane M itself. In the specific example described, the intermediate planes Pl and P2 are arranged at the same distance B from the edges 7a of the annular body 7 and thus from the middle plane M.
According to a variant (not shown) , the intermediate planes Pl and P2 are arranged at different distances from the corresponding edges 7a. In any case, the two intermediate planes Pl and P2 reciprocally separate an intermediate limit attachment zone 30 of the wire elements 21 from two side zones 31 and 32, which are free from any structural connection with the wheel rim 4, and thus extend freely and protrudingly from the corresponding intermediate planes Pl and P2, unlike the anchoring solution on the middle plane M where such side zones 31 and 32 extend from the middle plane M itself.
The variant shown in figure 5 differs from the solution, shown in figure 4 and just described in that a further intermediate crown 35 of fastening portions 36 arranged between the two flanges 6 is provided in addition to the two crowns 19 of attachment elements 20, through which a further connected, continuous wire element 21 extends, as the other wire elements 21, to the attachment elements 20 laying on the intermediate planes Pl and P2.
Regardless of the number of crowns of attachment portions and of the number and relative arrangement of the crowns 19 of attachment elements 20 in the mentioned intermediate attachment band 30, the wire elements 21 are always connected to the annular body 7 within the intermediate annular band, the boundaries of which are always spaced by a predetermined amount from the opposite axial edges 7a of the annular body 7 itself, so that the annular body 7 always has two annular axial end portions free from any structural connection to the wheel assembly 4. From the above, it is apparent that the specific constructing mode of the described wheel assembly 1 and, specifically, the fact of directing the actions exchanged between the tread 8 and the wheel rim 5 along converging directions towards an intermediate annular band of the annular body 7 spaced from both axial end edges 7a of the annular body 7 itself allows, in the field of the so-called 'airless' wheel assemblies, to make a wheel assembly with a high slip rigidity, a good radial rigidity, a high durability in terms of treadwear given a very light weight and an evident manufacturing ease.
More specifically, the construction features of the described wheel assembly 1 are, in essence, consequent to the fact that opposite axial end portions of the annular body 7, and thus of the tread 8, are no longer connected to the wheel rim 4 as in the known solutions, but are connected to an intermediate zone of the annular body 7, thus leaving the side portions arranged on axially opposite sides of the mentioned intermediate portion free from the mentioned structural connection.
With explicit reference to the slip stiffness, the anchoring of the intermediate portion of the annular body 7 makes the contrast of the lateral slip of the tread more effective. This is confirmed by the experimental curves shown in figure 7, wherein the curve H indicates ' the variation of the side displacement according to the variation of the side load in the case of the described wheel assembly 1, while the curve K indicates the variation of the side displacement according to the variation of the side load in the case in which the axial end portions are connected to the wheel rim, such as in the known wheel assemblies. Furthermore, the specific anchoring on the middle plane M produces an instantaneous virtual hinge for each anchoring point which allows the annular portion 7, and thus the tread 8, to rotate about an axis orthogonal to the axis 3 of the wheel assembly 1. In other words, upon oscillations of the wheel rim 4 about the mentioned longitudinal axis, the tread 8 is kept always essentially parallel to the rolling plane of the tread 8 itself .
Furthermore, the connection of the wheel rim 4 in the intermediate position of the tread allows to keep the tread 8 essentially λ flat', i.e. not curved, even in the presence of high side loads. In such a condition, the bending moment of inertia of the annular body with respect to an axis parallel to the rolling axis is clearly lower than a traditional omega- shaped tyre. Since such a bending moment of inertia opposes to the bending which the tread is subject to when is rolling, it results that the described wheel assembly 1 has a clearly low rolling friction, again as compared to traditional wheel assemblies . Having a tread which is kept practically flat is translated into an optimization of the contact pressure, which takes reduced average values as compared to the case of a traditional tyre, and into the fact that the shape of the tyre footprint is either quite or very close to a rectangular shape.
The particular mode used to make the stiffening portion 10 associated to the particular seam mode of the annular body 7 onto the wheel rim allow to overcome obstacles of different shape and size generating variations of vertical and longitudinal load on the vehicle hub, which variations are considerably lower than those generated by a traditional tyre. This is confirmed by the experimental curves shown in the chart in figure 6 wherein the curve indicated by letter T denotes the pattern of the vertical component on the hub according to time variations while overcoming an obstacle in the case of a traditional tyre, whereas the curves L and M denote the patterns of the vertical components on the hub in the case of two different wheel assemblies made according to the present invention with different wire elements.
Furthermore, a minimum amount of elastomeric material, specifically of reinforced elastomeric material, is used in the described wheel assembly, again as compared to traditional tyres, considerably reducing the problem of the disposal of the worn parts , which may be further facilitated by covering the worn parts instead of replacing the whole wheel assembly.
Finally, ' the use of the particular seam of the annular rim in conjunction with the particular construction mode of the reinforcing belt 10 made of elastomeric material allows to eliminate all metal tubular reinforcing bodies, thus solving the problems of size, weight and costs connected to the presence of such a reinforcing part . From the above it is apparent that changes and variations may be made to the described wheel rim assembly 1 without departing from the scope of protection defined by claim 1.
Specifically, the l seam' of the intermediate portion of the annular body to the wheel plate may be made by arranging the wire element or another equivalent elongated element, e.g. of the tape type, along different paths, but always so that the exchanged action are directed along inclined directions which essentially and reciprocally intersect on the annular body or in a position close to the same.
Furthermore, the elastomeric stiffening portion 10 of the tread 8 could be made in a different manner from that described, and similarly the shape of the tread 8 could also be different.